/*
 *                               POK header
 *
 * The following file is a part of the POK project. Any modification should
 * be made according to the POK licence. You CANNOT use this file or a part
 * of a file for your own project.
 *
 * For more information on the POK licence, please see our LICENCE FILE
 *
 * Please follow the coding guidelines described in doc/CODING_GUIDELINES
 *
 *                                      Copyright (c) 2007-2021 POK team
 */

/* s_cbrtf.c -- float version of s_cbrt.c.
 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
 */

/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunPro, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice
 * is preserved.
 * ====================================================
 */

#ifdef POK_NEEDS_LIBMATH

#include "math_private.h"
#include <libm.h>
#include <types.h>

/* cbrtf(x)
 * Return cube root of x
 */
static const unsigned B1 = 709958130, /* B1 = (84+2/3-0.03306235651)*2**23 */
    B2 = 642849266;                   /* B2 = (76+2/3-0.03306235651)*2**23 */

static const float C = 5.4285717010e-01, /* 19/35     = 0x3f0af8b0 */
    D = -7.0530611277e-01,               /* -864/1225 = 0xbf348ef1 */
    E = 1.4142856598e+00,                /* 99/70     = 0x3fb50750 */
    F = 1.6071428061e+00,                /* 45/28     = 0x3fcdb6db */
    G = 3.5714286566e-01;                /* 5/14      = 0x3eb6db6e */

float cbrtf(float x) {
  float r, s, t;
  int32_t hx;
  uint32_t sign;
  uint32_t high;

  GET_FLOAT_WORD(hx, x);
  sign = hx & 0x80000000; /* sign= sign(x) */
  hx ^= sign;
  if (hx >= 0x7f800000)
    return (x + x); /* cbrt(NaN,INF) is itself */
  if (hx == 0)
    return (x); /* cbrt(0) is itself */

  SET_FLOAT_WORD(x, hx); /* x <- |x| */
                         /* rough cbrt to 5 bits */
  if (hx < 0x00800000)   /* subnormal number */
  {
    SET_FLOAT_WORD(t, 0x4b800000); /* set t= 2**24 */
    t *= x;
    GET_FLOAT_WORD(high, t);
    SET_FLOAT_WORD(t, high / 3 + B2);
  } else
    SET_FLOAT_WORD(t, hx / 3 + B1);

  /* new cbrt to 23 bits */
  r = t * t / x;
  s = C + r * t;
  t *= G + F / (s + E + D / s);

  /* retore the sign bit */
  GET_FLOAT_WORD(high, t);
  SET_FLOAT_WORD(t, high | sign);
  return (t);
}

#endif
